Fiber composite materials include reinforcing fibers embedded in a matrix material. One example of a fiber composite material is a carbon fiber composite (CFC), which includes reinforcing carbon fibers embedded in a matrix material. CFCs may exhibit a variety of desired properties, such as high temperature stability, high thermal resistance, high mechanical integrity, light weight, corrosion resistance, and desired electrical and magnetic properties. By way of nonlimiting example, CFCs may exhibit a greater strength at a lower overall weight than metal materials. CFCs can thus be used to form a number of industrial and military structures including, for example, aerospace, marine, and automotive structures requiring one or more of the aforementioned properties.
Structures formed of composite materials have been coupled together to form components of rocket motors, such as rocket motor casings. However, fiber composite materials may exhibit an increased stress concentration at locations proximate the fasteners (e.g., bolts, rods, pins, etc.) used to couple the fiber composite material structures together. Accordingly, the resulting assembly may exhibit a low bearing strength at locations proximate the fasteners. To overcome such problems, it is known to manufacture fiber composite material structures to have an increased thickness at locations where the fiber composite material structure will be coupled to another material structure (e.g., another fiber composite material structure). In some instances, the fiber composite materials of such structures may be two to three times thicker proximate the fastener regions than in other regions thereof. Unfortunately, increasing the thickness of the fiber composite materials proximate the fastener regions undesirably increases an overall weight of a fiber composite material assembly formed of and including the fiber composite material structures.
Methods of improving the bearing strength of a fiber composite material without increasing the thickness thereof include placing thin metallic structures (e.g., thin metal plies) in the fiber composite material to form a hybrid metal composite structure comprising the fiber composite material and the metal plies. The metal plies may reduce an overall weight of the structure by as much as about 30 percent. In some applications, this reduction in weight may correspond to a reduction in thousands of pounds. However, fabrication of composite structures including metal plies is difficult due to, among other things, poor adhesion of the metal ply surfaces to the resin of the fiber composite material. Poor adhesion may result in delamination of the metal ply from the hybrid metal composite structure and failure of the hybrid metal composite structure.